The present invention relates to an apparatus, method and program for alarming abnormality in tire air-pressure.
Among tires, it is difficult to determine decrease in tire air-pressure, in particular such as a run-flat tire which allows traveling even if air-pressure therein is zero. In the case where a vehicle travels at high velocity with decreased air-pressure, there has been a problem that a tire may blow out.
In view of this, various methods to detect decrease in tire air-pressure have been investigated. In Japanese Unexamined Patent Publication No. 305011/1988, it is disclosed a method for detecting a deflated tire from wheel velocities of four wheel tires provided on a vehicle by using a tire deflation warning system (DWS). According to this method, by utilizing a phenomenon in which rotational velocity becomes faster due to the decrease in substantial rotational radius when tire air-pressure is decreased, an air-pressure in a certain tire on a wheel is detected to be decreased from a difference between the sum of the wheel rotational velocity of a pair of tires on a diagonal line and the sum of the wheel rotational velocity of a pair of tires on the other diagonal line as well as a difference between rotational velocity of a certain wheel and an average value of rotational velocities of four wheels.
However, there are cases in which a rotational velocity of a certain wheel becomes slower compared with those of the other wheels not only under unusual conditions such as offset load on a vehicle or providing a snow chain on one wheel, but also under condition for cornering of a vehicle. Under such traveling conditions, in the case where air-pressure is detected by the above-mentioned method for detecting decrease in tire air-pressure, there are cases in which a deflation alarm is issued even when air-pressure decrease is not generated in fact. There has been a problem that such unnecessary alarm results in making an erroneous decision and incurring unnecessary costs (maintenance) to a driver.
An object of the present invention is to provide an apparatus, method and program for alarming abnormality in tire air-pressure which allows detecting abnormality of a tire even under unusual traveling conditions such as offset load on a vehicle or providing a snow chain on one wheel.